Conventionally, structures of motors used for electric power steering devices have been devised, and a stage-skew structure is disclosed in Patent Documents 1 and 2, for example.
Patent Document 1 discloses that each divided rotor core is rotationally displaced from each other by 6 degrees in one direction around the central axis line of the rotational shaft such that magnetic skew by 60 degrees in electric angle is kept between a magnetic pole of a rotor core and a magnetic pole of a stator, thereby eliminating a torque ripple wave for electric angle twelfth order occurring in a brushless motor.
Patent Document 2 discloses that a brushless motor having a rotor with 2n-number of magnetic poles and a stator with 3n-number of slots has a step-skew structure in which the magnetic poles of the rotor are formed by segment magnets arranged at three stages in the axial direction, and the magnets at the adjacent stages are displaced from each other in the circumferential direction such that a skew angle θ skew of the segment magnets is set at 60 to 75 degrees in electric angle, thereby improving robustness, and improving output as compared to a conventional motor having a rotor-skew structure using a ring magnet.